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Dental Materials > Gypsum Products > Flashcards

Gypsum Products Flashcards

0
Q

Rocks or solid particles which were ground to powder form and the heated

A

Gypsum

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1
Q

Example of gypsum products

A
  1. Orthoplaster
  2. Dental stone
  3. Plaster of paris
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2
Q

Gypsum produced for dental applications

A

Calcium sulfate dihydrate

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3
Q

Process of heating gypsum

A

Calcination

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4
Q

Heating is done in a kettle or an open bath

A

Open calcination

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5
Q

Stirring in open calcination

A

110 degrees celcius to 120 degrees celsius or

230 degrees farenheit to 250 degrees fahrenheit

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6
Q

Product of open calcination

A

Beta hemihydrate or plaster of paris

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7
Q

Beta hemihydrate is also known as

A

Plaster of paris

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8
Q

Consists of large, irregularly shaped orthorombic crystal particles with capillary pores

A

Plaster of paris

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9
Q

Spongy and irregular in shape

A

Crystals

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10
Q

Done in an autoclave and there’s a pressure involved

A

Closed calcination

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11
Q

Pressure and temperature of closed calcination

A

16 psi

120 degrees celcius to 130 degrees celcius

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12
Q

Product of closed calcination

A

Alpha hemihydrate or dental stone

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13
Q

Alpha hemihydrate is also known as

A

Dental stone

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14
Q

Consists of smaller, regularly shaped crystalline particles in the form of rods or prisms

A

Dental stone

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15
Q

Crystals are prismatic and more regular in shape

A

Dental stone

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16
Q

Used to take impression

A

Impression/ soluble plaster

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17
Q

Used to make study cast or model for records purposes

A

Plaster of paris

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18
Q

Stronger than plaster of paris

A

Dental stone ( class 1 )

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19
Q

Used as working cast that can withstand forces applied

A

Dental stone (class 1)

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20
Q

Stronger than class 1 dental stone

A

Dental stone high strength or class 2 dental stone

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21
Q

Used as working die for crown restoration and other treatments needing accurate measurements

A

Dental stone high strength (class 2 dental stone)

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22
Q

Refers to single tooth or several teeth

A

Die material

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23
Q

Used as inventing medium to compensate the high shrinkage of metals such as chrome cobalt ion

A

Dental stone high strength high expansion

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24
Q

Other uses of gypsum products:

A
  1. Used for ceramics
  2. Used for medical purposes: cast for broken bones
  3. Used to stabilize articulation between upper and lower cast
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25
Q

Addition of powder to water until the mixing time is completed

A

Mixing time

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26
Q

Time of mechanical mixing

A

20 to 30 seconds

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27
Q

It requires atleast a minute to obtain a smooth mix

A

Hand spatulation

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28
Q

Time available to use a workable mix

A

Working time

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29
Q

Maintained to perform one or more tasks

A

Uniform consistency

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30
Q

Measured from the time of mixing to the point where the consistency is no longer acceptable for the product’s intended purpose

A

Working time

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31
Q

Time adequate for working time

A

3 minutes

32
Q

Time that elapses from the beginning of mixing until the material hardens

A

Setting time

33
Q

Measured by penetration tests

A

Setting time

34
Q

Types of penetration test

A
  1. Vicat needle

2. Gilmore needle

35
Q

Measure initial setting time (1/4 lb)

A

Vicat needle

36
Q

Measures final setting time 1/4 and 1 lb

A

Gilmore needle

37
Q

Measured from the start of mixing until the 2nd increase of temperature

A

Initial setting time

38
Q

Time for initial setting time

A

7-13 minutes

39
Q

Measured from the start of mixing until the 2nd decrease of temperature

A

Final setting time

40
Q

Time for final setting time

A

20 minutes

41
Q

Significance of finding initial setting time

A
  1. Time to trim off extra plaster or stone that overflowed

2. To prevent the breakage of the cast

42
Q

Significance of finding final setting time

A
  1. To prevent premature separation

2. To prevent powdery casts

43
Q

Manipulation of gupsum products:

A

✔️ know the WP ratio
✔️ put the water first then the powder in the bowl
✔️ let them settle for 30 seconds to remove air
✔️ mix it using rotatory motion at 120 rpm for 1 1/2 minutes
✔️ tap the mixture to released entrapped air

44
Q

Theoretical factors affecting setting time

A
  1. Number of nuclei
  2. Solubility of the hemihydrate
  3. Rate of crystal growth
45
Q

Number of nuclei crystallization

A

Greater number of nuclei, decrease ST, the shorter

Lesser number of nuclei, increase ST, the longer

46
Q

Solubility of the hemihydrate

A

More soluble, the faster the ST

47
Q

Rate of crystal growth

A

Faster rate of crystallization, faster ST

48
Q

Practical factors affecting setting time

A
  1. Presence of impurities
  2. Fineness
  3. WP ratio
  4. Mixing time
  5. Temperature
  6. Accelerators and retarders
49
Q

Decrease ST =

A

Faster setting

50
Q

Particle size and shape of crystals

A

Fineness

51
Q

Smaller crystals, more soluble, faster

A

Fineness

52
Q

Too thin

A

Prone to air bubbles

53
Q

Too thick

A

Not all powder will be mixed with water

54
Q

WP ratio

A

More water, less powder, longer setting time

Less water, more powder, shorter setting time

55
Q

Mixing time

A

2 minutes

56
Q

Longer time, faster mixing rpm, faster setting time

A

Mixing time

57
Q

Up to 50 degrees celcius

A

Accelerator

58
Q

Above 50 degrees celcius

A

Retarder

59
Q

Most practical way for a clinician to control setting time

A

Altering temperature

60
Q

Tend to remove the surface coating of crystals making them more soluble to water

A

Accelerators

61
Q

Best accelerator regardless of concentration

A

K2SO4

62
Q

Tend to create surface coating of crystals making them less soluble to water

A

Retarders

63
Q

Examples of retarder

A
  1. Borax
  2. Nitrates
  3. Citrates
  4. Higher conc of NaCl and Na2SO4
64
Q

Plaster impression
WP ratio:
Psi:
Setting expansion:

A

.50-.75
290-870
0-.15 %

65
Q

Plaster of paris
WP ratio:
Psi:
Setting expansion

A

.45-.50
1300
0-.30%

66
Q

Dental stone
WP ratio:
Psi:
Setting expansion

A

.28-.30
3000
0-.20%

67
Q

Die stone
WP ratio:
Psi:
Setting expansion

A

.22-.24
5000
0-.10%

68
Q

Dental stone high strength hig expansion
WP ratio:
Psi:
Setting expansion

A

.18-.22
7000
.10-30%

69
Q

Why is that the WP ratio for plaster impression is high?

A

So that it can flow more because it’s for impression taking

70
Q

Factors affecting compressive strength

A
  1. Shape and size of the particles
  2. WP ratio
  3. Mixing technique
  4. Use of chemical modifiers
71
Q

Factors affecting setting expansion

A
  1. WP ratio
    - increase water, decrease setting expansion
    - increase powder, increase setting expansion
  2. Addition of chemical modifiers
    - potassium sulfate
72
Q

Accelerators

A

ST: -
SE: -
S : -

73
Q

Retarders

A

ST: +
SE: -
S: -

74
Q

Particle size

A

ST: +
SE: +
S: +

75
Q

WP ratio

A

ST: +
SE: -
S: -

76
Q

Spatulation

A

ST: -
SE: +
S: -

77
Q

Temperature

A

ST: -
SE: 0
S: 0

78
Q

Care for gypsum products

A
  1. Put it in a cool dry place

2. Place it in air tight container

Dental Materials (2 decks)

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